The two primary systems for centering wheels on the hubs of motor vehicles are stud piloted and hub piloted. Dual wheel assemblies are used on many large vehicles such as buses and semi rigs. The dual wheel assemblies, with a stud piloted system, require an inner cap nut on each stud to center and secure the inner wheel and an outer cap nut on each stud to center and secure the outer wheel. Dual wheel assemblies, with a hub piloted system, use a one or two piece flange nut on each stud to secure both the inner and outer wheels. An “18 wheeler” has on the tractor a front steer axle with two single wheel assemblies and two rear axles each having two dual wheel assemblies, and on the trailer two rear axles each having two dual wheel assemblies, for a total of two single wheel assemblies and eight dual wheel assemblies. With ten studs per hub, 180 nuts are required with a stud piloted system compared to the 100 nuts required with a hub piloted system.
A hub piloted system provides material and labor cost reduction through the elimination of the inner cap nut. Other benefits of hub piloted systems include elimination of bolt hole chamfer wear, greater clamping force for a given torque, reduction in nut wear and nut replacement, and more consistent nut torque retention. In hub piloted systems, the hubs generally have a plurality of circumferentially spaced hub pilots that center the hub aperture of the wheel. There is generally a small clearance between the hub pilots on the hub and the hub aperture on the wheel to facilitate wheel installation. When the wheel is mounted on the hub, gravity pulls the wheel down, and the wheel is not precisely centered.
U.S. Pat. No. 2,017,114 to Winchester discloses a nut assembly with a skirt that extends through the bolt aperture of the outer wheel and into the bolt aperture of the inner wheel of a dual wheel assembly. U.S. Pat. No. 6,070,946 to Holmes teaches that the skirt of Winchester that extends through the bolt aperture of the outer wheel and into the bolt aperture of the inner wheel can create undue difficulty in installing the nut assembly and jamming of the nut assembly due to relative movement of the inner and outer wheels. Holmes discloses a skirted nut that extends only into the bolt aperture of the outer wheel of a dual wheel assembly. U.S. Pat. No. 6,715,843 to Teague discloses a sleeve for centering a brake drum and a single wheel.